1,560 research outputs found
Size and asymmetry of the reaction entrance channel: influence on the probability of neck production
The results of experiments performed to investigate the Ni+Al, Ni+Ni, Ni+Ag
reactions at 30 MeV/nucleon are presented. From the study of dissipative
midperipheral collisions, it has been possible to detect events in which
Intermediate Mass Fragments (IMF) production takes place. The decay of a
quasi-projectile has been identified; its excitation energy leads to a
multifragmentation totally described in terms of a statistical disassembly of a
thermalized system (T4 MeV, E4 MeV/nucleon). Moreover, for
the systems Ni+Ni, Ni+Ag, in the same nuclear reaction, a source with velocity
intermediate between that of the quasi-projectile and that of the quasi-target,
emitting IMF, is observed. The fragments produced by this source are more
neutron rich than the average matter of the overall system, and have a charge
distribution different, with respect to those statistically emitted from the
quasi-projectile. The above features can be considered as a signature of the
dynamical origin of the midvelocity emission. The results of this analysis show
that IMF can be produced via different mechanisms simultaneously present within
the same collision. Moreover, once fixed the characteristics of the
quasi-projectile in the three considered reactions (in size, excitation energy
and temperature), one observes that the probability of a partner IMF production
via dynamical mechanism has a threshold (not present in the Ni+Al case) and
increases with the size of the target nucleus.Comment: 16 pages, 7 figures, accepted for publication on Nuclear Physics
Inauguration of the Centro 3R for the promotion of 3Rs principles in teaching and research.
the first European interuniversity center dedicated to promoting 3Rs principles in teaching and research was inaugurated in Pisa, Italy on March 14, 2018. The Centro 3R was spearheaded
by the Universities of Pisa and Genoa. Membership is open to all Italian universities and agreements for twinning across Europe and other countries are being pursued. the Centro\u2019s mission to promote rational and scientific thinking in experimental science through a multidisciplinary teaching and research approach inclusive of all 3Rs as a means to accelerate the R of
replacement. The projects to develop an open resource-sharing web platform and interdisciplinary elective courses were also mentioned
Effects of recreational scuba diving on Mediterranean fishes: evidence of involuntary feeding?
Despite a large body of literature assessing the impacts of recreational scuba diving on marine habitats, little attention has been paid to the potentially harmful effects this has on fishes. The aim of this study was the assessment of the immediate response of different fish species to diversâ activities. A decrease of fishesâ natural diffidence towards divers is shown, probably due to an enhanced availability of their prey as a result of diversâ contacts with the substrate
Isotopic Composition of Fragments in Nuclear Multifragmentation
The isotope yields of fragments, produced in the decay of the quasiprojectile
in Au+Au peripheral collisions at 35 MeV/nucleon and those coming from the
disassembly of the unique source formed in Xe+Cu central reactions at 30
MeV/nucleon, were measured. We show that the relative yields of neutron-rich
isotopes increase with the excitation energy in multifragmentation reaction. In
the framework of the statistical multifragmentation model which fairly well
reproduces the experimental observables, this behaviour can be explained by
increasing N/Z ratio of hot primary fragments, that corresponds to the
statistical evolution of the decay mechanism with the excitation energy: from a
compound-like decay to complete multifragmentation.Comment: 10 pages. 4 Postscript figures. Submitted to Physical Review C, Rapid
Communicatio
Ageing and creeping management in major accident plants according to seveso III directive
The focus of this paper is the management of critical equipment ageing within the context of lower and upper tier Seveso process plants, with a peculiar insight into the effectiveness of safety management systems in setting-up reliable procedure for critical element identification. Recent research studies in fact evidenced that in Europe nearly 50% of major 'loss of containment' events, arising from technical plant failures, were primarily due to ageing plant mechanisms such as erosion, corrosion and fatigue. The critical ageing elements should be included in maintenance, inspection and periodic monitoring programs in relation to their reliability, as assumed in the risk assessment and their lifetime or frequency ranges, based on their operational experience. This paper will accurately discuss how the issue of ageing is currently handled in the process industry. The methodology builds on the critical results of actual findings from the inspections on the safety management systems of major accident plants, which were performed by a working group. The primary objective is to stimulate the introduction of effective ageing management changes into the safety management of companies, by taking advantages of findings of the previous assessment and establishing proper and effective audits
Plastic adjustments of biparental care behavior across embryonic development under elevated temperature in a marine ectotherm
Phenotypic plasticity in parental care investment allows organisms to promptly respond to rapid environmental changes by potentially benefiting offspring survival and thus parental fitness. To date, a knowledge gap exists on whether plasticity in parental care behaviors can mediate responses to climate change in marine ectotherms. Here, we assessed the plasticity of parental care investment under elevated temperatures in a gonochoric marine annelid with biparental care, Ophryotrocha labronica, and investigated its role in maintaining the reproductive success of this species in a warming ocean. We measured the time individuals spent carrying out parental care activities across three phases of embryonic development, as well as the hatching success of the offspring as a proxy for reproductive success, at control (24â) and elevated (27â) temperature conditions. Under elevated temperature, we observed: (a) a significant decrease in total parental care activity, underpinned by a decreased in male and simultaneous parental care activity, in the late stage of embryonic development; and (b) a reduction in hatching success that was however not significantly related to changes in parental care activity levels. These findings, along with the observed unaltered somatic growth of parents and decreased brood size, suggest that potential cost-benefit trade-offs between offspring survival (i.e., immediate fitness) and parents' somatic condition (i.e., longer-term fitness potential) may occur under ongoing ocean warming. Finally, our results suggest that plasticity in parental care behavior is a mechanism able to partially mitigate the negative effects of temperature-dependent impacts
Causal analysis of positive Reaction Systems
Cause/effect analysis of complex systems is instrumental in better understanding many natural phenomena. Moreover, formal analysis requires the availability of suitable abstract computational models that somehow preserve the features of interest. Our contribution focuses on the analysis of Reaction Systems (RSs), a qualitative computational formalism inspired by biochemical reactions in living cells. The primary challenge lies in dealing with inhibition mechanisms. On the one hand, inhibitors enhance the expressiveness of the computational abstraction; on the other hand, they can introduce nonmonotonic behaviors that can be computationally hard to deal with in the analysis. We propose an encoding of RSs into an equivalent formulation without inhibitors (called Positive RSs, PRSs for short) that is easier to handle, because PRSs exhibit monotonic behaviors. The effectiveness of our transformation is witnessed by its impact on two different techniques for cause/effect analysis. The first, called slicing, allows detecting the causes of some unforeseen phenomenon by reasoning backward along a given computation. Here, PRSs can be exploited to improve the quality of the analysis. The second technique, predictor analysis, is addressed by introducing a novel tool called MuMa, which is based on must/maybe sets, whence the tool name, an original abstraction for approximating ancestor formulas. MuMa exploits PRSs to improve the performance of the analysis
Quantitative extensions of reaction systems based on SOS semantics
Reaction systems (RSs) are a successful natural computing framework inspired by chemical reaction networks. A RS consists of a set of entities and a set of reactions. Entities can enable or inhibit each reaction and are produced by reactions or provided by the environment. In this paper, we define two quantitative variants of RSs: the first one is along the time dimension, to specify delays for making available reactions products and durations to protract their permanency, while the second deals with the possibility to specify different concentration levels of a substance in order to enable or inhibit a reaction. Technically, both extensions are obtained by modifying in a modular way the Structural Operational Semantics (SOS) for RSs that was already defined in the literature. Our approach maintains several advantages of the original semantics definition that were: (1) providing a formal specification of the RS dynamics that enables the reuse of many formal analysis techniques and favours the implementation of tools, and (2) making the RS framework extensible, by adding or changing some of the SOS rules in a compositional way. We provide a prototype logic programming implementation and apply our tool to three different case studies: the tumour growth, the Th cell differentiation in the immune system and neural communication
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